1. Field of the Invention
The present invention relates to an organic light emitting device, and more particularly, to a white organic light emitting device with improved color shift characteristics and improved efficiency according to viewing angle changes by controlling conditions for optical path in organic material layers disposed between a cathode and an anode or adjusting interior or exterior thicknesses of the organic material layers, and a display device using the same.
2. Discussion of the Related Art
In recent years, the field of displays that visually express electric information signals has rapidly developed with the advent of the information age. Correspondingly, a variety of flat display devices having excellent performance, such as slim design, lightweight, and low power consumption, have been developed and rapidly replaced conventional cathode ray tubes (CRTs).
Detailed examples of flat panel display devices may include liquid crystal display devices (LCDs), plasma display panels (PDPs), field emission display devices (FEDs), and organic light emitting devices (OLEDs).
Among the aforementioned ones, the OLED has competitiveness because it does not need a separate light source and realizes a compact device design and vivid color.
In such OLEDs, formation of an organic light emitting layer is necessary. Conventionally, deposition using a shadow mask has been used therefor.
However, if a large-area shadow mask is used, the shadow mask sags due to heavy weight thereof so as not to be used multiple times, and defects are generated in the formation of an organic light emitting layer pattern. Thus, alternative approaches thereto are required.
As one approach replacing such a shadow mask, a tandem white organic light emitting device (hereinafter, referred to as a ‘white organic light emitting device’) is introduced, and the white organic light emitting device will be described.
The white organic light emitting device is manufactured by respectively depositing layers between a cathode and an anode on one another without using a mask upon formation of a light emitting diode. In other words, organic layers including organic light emitting layers are sequentially formed by depositing different materials in a vacuum state. In addition, the white organic light emitting device includes different light emitting layers emitting a plurality of colored light beams between the cathode and the anode. Since charge generation layers are respectively disposed between two adjacent light emitting layers, stacks are divided based on each light emitting layer as a basic structure.
Such a white organic light emitting device emits light by a combination of light beams emitted from a plurality of light emitting layers respectively including light emitting materials with different photoluminescence (PL) peaks at each corresponding wavelength and disposed at different positions of the device rather than using only a single material. In addition, for example, the white organic light emitting device may also be implemented by laminating a stack including a fluorescent light emitting layer and a stack including a phosphorescent light emitting layer.
However, when using known light emitting materials, as a viewing angle increases, a brightness reduction rate of the fluorescent light emitting layer is greater than that of the phosphorescent light emitting layer. Thus, as viewing angle increases, warmer white color coordinates having a lower color temperature are obtained in the white organic light emitting device. Viewers may recognize a color change according to viewing angle changes if the white organic light emitting device has such warmer white color coordinates. Thus, efforts to improve thereon have been conducted.